This invention relates generally to the field of face finishing, and more particularly to a process and apparatus for angularly sueding a textile web containing fill and warp yarns. More specifically, the invention concerns a method of angularly abrading a textile web in order to produce effective and improved sueding within the web and decrease the potential for noticeable defects within the resultant textile. An apparatus for producing such effects is also provided.
There are several types of spun yarns commonly used in the construction of woven fabrics. Among the most common, and familiar to those versed in the art, are ring spun, open-end spun (OES), air-jet spun (AJS), and roller jet spun (RJS) yarns. Ring spun yarns consist of generally helically wound fibers which, when woven into fabrics, exhibit excellent hand and fabric containing them becomes stiffer and harsher, as increased twist reduces fiber-to-fiber mobility. OE yarns, compared to ring spun yarns, are more disorganized and have a lower twist. The fiber bundle comprising the yarn is compacted by the presence of tightly wound wrapper fibers, which are nearly perpendicular to the axis of the yarn. As the yarn structure of OE yarns is less organized than that of ring spun yarns, the OE yarn exhibits a larger diameter than that of a ring spun of an equivalent denier. The larger size of the OE yarn, coupled with the lack of mobility of the fibers, because of the pressure imparted by the wrapper fibers, results in a stiffer fabric, in spite of the lower twist as compared to ring spun yarns. The tightly wound wrapper fibers also cause the surface of the fabric to be harsh and scratchy to the touch. The relative fiber immobility makes it difficult to enhance the fabric by needling with hydraulic jets, as these yarns cannot easily blossom when constricted by the wrapper fibers. In the same way, wrapper fibers reduce the effectiveness of pneumatic vibratory softening as disclosed in my U.S. Pat. No. 4,918,795, entirely incorporated herein by reference. As the wrapper fibers are not aligned with the axis of the yarn, they do not contribute to fabric strength, and fabrics constructed of yarns containing wrapper fibers are generally not as strong as fabrics constructed of ring spun yarns. AJS and RJS yarns are similar to OE yarns, but have core fibers with little or no twist, and the integrity of the yarn entirely depends upon the presence of the wrapper fibers. Without the fiber-to-fiber friction created by the pressure exerted by the wrapper fibers, the yarn would have no tenacity and could not be woven into fabrics. Once a fabric has been woven, yarn-to-yarn pressures are sufficient to create frictional forces between fibers, and the wrapper fibers are no longer necessary for strength. Loosening or cutting wrapper fibers, by various means such as by sanding or napping, so as to improve the hand and other properties, without substantial cutting of the load bearing fibers, can dramatically improve the hand and surface touch of the fabric, allow the fabric to blossom when hydraulically needled or to soften when pneumatically vibrated, as well as improve adhesion to coatings, without degrading fabric strength. Other methods of sanding and abrading textile fabrics are known, such as that disclosed in U.S. Pat. No. 5,058,329, to Love et al., entirely incorporated herein by reference, however they are not effective in severing or sufficiently loosening the wrapper fibers within the fabric in order to create significant associated benefits resulting therefrom without also cutting load bearing fibers and substantially reducing the strength of the fabric.
While it is possible to cut the non-load bearing wrapper fibers in the yarns without substantially reducing the fabric tensile properties, as is disclosed in my U.S. patent applications Ser. No. 08/738,787 and 08/995,184, both entirely incorporated herein by reference, it is often desirable to achieve a sueded finish by means of various types of surface abrasion, wherein load bearing fibers are also cut. However, several problems may result from such a process.
One problem associated with such surface abrasion of textile webs is the possibility of producing streaks within the resultant fabric. These are relatively lighter or darker lines that appear in the warp direction. While these may be due to fabric or yarn irregularities, they may also occur due to random variation in the grit particles. If a particularly large or aggressive particle is present, more fibers will be cut, and lighter colored fibers in the yarn core may be exposed, producing a streak. One method of mollifying the effect of individual grit particles is to make the abrasive drum very large so that the effect of a single grit particle is not continuous. However this method reduces the pressure of the fabric against the treatment roll, requiring either relatively coarse grit, or some other means to create pressure, such as through the utilization of flaps, backup rolls, or air pressure. Another method is to make the streak more difficult to observe by oscillating the treatment rolls along the rotational axis, creating a sinusoidal pattern on the fabric, so that the effect of single grit particles spread out. Oscillation is often used in multi-roll treatment machines, with the oscillations timed so as not to be superimposed.
Another common problem with all abrasive processes is that the cutting of fibers reduces the tensile properties of the fabric, regardless of yarn type. Also, except in the case of warp-faced fabrics, there is more interaction of the abrasive particles with the fibers of the fill yarns, since these fibers are more perpendicular to the movement of the abrasive particles as compared to the fibers of the warp yarns. This interaction results in relatively greater abrasion and strength degradation to the fill yarns, and may result in the shifting of fill yarns relative to warp yarns in the fabric. Compounding this problem is that, for reasons of weaving economy, many fabrics are more lightly constructed in the fill direction and therefore are initially weaker in that direction. Fibers of warp yarns, in particular filament yarns, are more difficult to cut where there is a parallel orientation of the abrasive particles and the filaments. Thus, a method of abrasively treating a web so as to retain fill strength while also avoiding a streaky appearance is needed. The present invention solves these problems in a manner not disclosed in the known prior art while producing a textile potentially having fewer noticeable defects than by other heretofore employed methods.
A method and apparatus for providing improved and efficient sueding and sanding of fill and warp yarns through loosening, cutting, and abrading a web of textile fabric is contemplated within this invention. The textile fabric web is directed under tension around at least one pair of rotatable tubes (rolls) (approximately from two to twenty-four inches in diameter) coated with abrasive particles bonded directly to the roll face and disposed at an abrasion angle. The rotational axis of a roll is parallel to the plane of the web, while the abrasion angle is 90 degrees minus the counter-clockwise angle that a tube axis makes relative to the direction of web travel. If a roll axis is oriented in the traditional sueding direction, perpendicular to the web direction, then the abrasion angle is 0 degrees. The preferred abrasion angle for angular sueding ranges from about 5 degrees to about 60 degrees and more preferably from about 10 degrees to about 45 degrees. Preferably, rolls are used in pairs with each tube of a pair position at the same abrasion angle. The abrasion angle may be positive or negative, and there may be more than one abrasion angle if multiple pairs are employed. The abrasion angle is different from the wrap angle, which is here used in the traditional sense to refer to the included angle of contact between the web and the roll. Preferred wrap angles range from 1 degree to 45 degrees, and preferably from about 2 degrees to 30 degrees.
The rolls are paired wherein one is a regressive roll and the other a progressive roll. By regressive it is meant that the roll has a rotational component in a direction opposite that of the direction of web travel, which tends to increase the subsequent tension of the web. By progressive, it is meant that the roll has a rotational component in the same direction as direction of web travel, with a surface speed faster than the web speed, which tends to decrease the subsequent tension of the web. The tension of the textile fabric web should exceed two (2) pounds per linear inch of web width (p.l.i.).
Therefore, the primary object of the invention is to provide a more balanced abrasive treatment of warp and fill yarns. Another object of the invention is to provide a higher level of sueding with the same retained fill tensile and tear properties. A further object of the invention is to provide a method of cutting the fibers of filament warp yarns. Yet another object of the invention is to provide an apparatus for angularly sueding a web. Still a further object of the invention is to provide a method of sueding that is inherently free of streaks. An additional object of the invention is to provide a method of sueding fabrics which are sensitive to shifting of the fill yarns.
Other objects and advantages of the present invention will become apparent from the following descriptions, taken in connection with the accompanying drawings, wherein, by way of illustration and example, an embodiment of the present invention is disclosed.